Duke Street Capital Oasis Holdings, provider of NHS and private dentistry trading as Oasis Healthcare, showed an increased turnover for the year ended 31 March 2012, £148.1m from £135.6m the previous year (up 9%).An operating profit of £1.1m (year to 31 March 2011: loss of £3.9m) became a loss after tax of £22.7m (year to…